Flotation of paper fibers



United States Patent 3,256,140 FLOTATION OF PAPER FIBERS Franz Poschmann, Ludwigshafen (Rhine), Germany, assignor to Badische Anilin- & Soda-Fabrik Aktiengesellschaft, Ludwigshafen (Rhine), Germany N0 Drawing. Filed May 1, 1962, Ser. No. 191,414 Claims priority, applicatistin G frmany, May 3, 1961,

6 Claims. ((31.162-190) I This invention relates to a new process for the flotation of paper fibers.

In the production of paper it is of great economic importance to recover the paper fibers present in the industrial water. Sedimentation and flotation are the main conventional methods of recovery. .Flotation has achieved the greater importance because considerably larger plant is required for sedimentation and consequently larger amounts of water, and moreover sedimentation requires considerably longer periods. Since for these reasons flotation facilitates manufacturing adaptations, it is the indispensable method for operation with frequent changes in the type of paper, especially with change in colored types of paper.

I The development of suitable flotation plant and methods is therefore an urgent problem in the technology of paper manufacture. Factors for successful flotation are an advantageous flow of water, an effective proportioning of air and especially the flotation chemicals. The agents effecting flocculation hitherto used have been neutral, acid and alkaline inorganic substances, for example diatomaceous earth, colloidal silicic acid, lime and alum and also anionic, cationic, amphoteric and non-ionic organic substances, such as sulfonic and carboxylic acids which lower the interfacial tension and compounds which contain amino groups, imino groups, quaternary amino groups or polyalkylene chains. The said groups may be present one or more times in a molecule so that the flotation agents may also be highly polymerized water-soluble compounds, such as polyvinylimidazole, polyacrylamide, polyethylenimine, polycondensates of polyamines and reaction products of epichlorohydrin with polycondensates containing amino groups, and also polyvinylamines and polyvinylammonium compounds as well as natural or chemically modified proteins.

The object of the invention is to provide a process for the flotation of paper fibers which is more rapid and more economical than the prior art methods.

I have'found that this object is achieved by using as flotation agent an ionic, preferably anionic, surface-active compound in combination with a water-soluble salt-like polymer whose monomer units are acrylamide and/or methacrylamide and a vinyl monomer of the general formula:

in which R denotes a hydrogen atom or a low molecular weight alkyl group, R R and R denote identical or different radicals, for example alkyl groups, hydroxyalkyl groups, cycloalkyl groups and groups which are connectedtogether and form with the nitrogen atom a heterocyclic fiveor six-membered non-aromatic ring, and in which Y denotes the equivalent of an acid radical.

The most suitable ionic surface-active compounds (referred to hereinafter as component I) are anionic surfaceactive compounds whose anion has a strongly hydrophobic portion of the molecule. Examples are simple fatty soaps, detergents and wetting agents, such as dodecylbenzene sulfonate, castor oil sulfonate, alkylnaphthalene sulfonates, alkyl sulfonates, products which are obtained by sulfiting unsaturated fatty acid esters, fatty alcohol sulfonates, fatty acid derivatives containing anionic groups, such as a condensate of a fatty acid chloride and methyltaurine, and polyhydroxyalkylation products containing anionic groups. It is preferable to use resin soaps (e.g., alkali metal salts of colophony) and especially modified resin soaps, such as reaction products of colophony (=abietic acid) with unsaturated carboxylic acids, for example maleic acid, as component I.

Amphoteric surface-active compounds, as for example betaine compounds of aminofatty acids, may be used as component I for the process according to this invention, and also cationic surface-active compounds, such as invert soaps, although not with such good results as anionic compounds.

Salt-like polymers, which are obtainable according to the process of British patent specification No. 887,900 (hereinafter referred to as component II) should contain between 1 and 100 mole percent of atleast one quaternary monomer polymerized into the same; suitable comonomers are acrylamide and/ or methacrylamide in amounts of 0 to 99 mole percent.

In the monomers of the above-mentioned formula, R may be a hydrogen atom or for example a methyl, ethyl, propyl or isopropyl group, Examples of R R and R are methyl, ethyl, propyl, butyl, isopropyl, tert.-butyl, amyl, dodecyl, hydroxyethyl and cyclohexyl groups; R and R may also be combined with the nitrogen atom to form a fiveor six-membered heterocyclic non-aromatic radical, for example to form aN-pyrrolidine, N -piperidine or N-morpholine radical. The anion Y has no ascertainable eifect on the success of the flotation; examples of Y are the acid residues of sulfuric acid, methylsulfuric acid, halogen hydracids, acetic acid, phosphoric acid and p-toluenesulfonic acid.

Examples of quaternary vinyl monomers of the said type are N,N-diethyl-N-methylmethacryloylaminomethyleneammonium-methyl sulfate (R =methyl;'

R =methyl; Y =methyl sulfate N,N,N-trimethylmethacryloylamidomethyleneammonium chloride pyrrolidinyl-N-methylacryloylamidomethyleneammonium' sulfate (R =H; R and R are joined together to form the pyrrolidine radical; R =methyl; Y /2 S0 Salt-like copolymers (component II) which are especially active are those which contain at least 10 mole percent of the quaternary compound and which have a K-value of more than 100. Advantageous results are obtained in general when the components I and II are used in about the same amounts by weight for the flotation.

dure is adoped; as a rule, it is not necessary to keep to a definite sequence in adding the components I and II, but it may be advantageous not to add all the flotation agent at once but in a number of portions. It is advantageous to use about equal amounts by weight of the components I and H, in generalamounts of 0.001 to 5% of each with reference to the fibrous material. If sufiicient amounts of polymer (component II) are present, spontaneous flotation can be achieved by using an excess of component I, about up to 50% with reference to the fibrous material. For the rest, the optimum conditions should be ascertained in each case, i.e., according to the flotation plant and the fibrous material to be separated; the amount of flotation agent to be used also depends on the surface, i.e., the fineness of grain of the paper fibers. Thus for example a smaller amount of component I is required in the case of fibers of sized papers because such papers already contain resin soaps. In some cases the coemployment of other substances may be advantageous; for example surface-active compounds which are not capable of being precipitated by metal ions promote flotation in the strongly acid range. The data is given in the examples later in the specification form a valuable guide to the discovery of these favorable conditions.

Within the temperatures occuring in practice, the process according to this invention exhibits no recognizable dependence on the temperature; similarly, it is practically independent of the pH-value. Effective flotation of all cellulosic bleached and unbleached paper fibers is possible therewith even when they have already frequently passed through the process of paper manufacture, and the process is independent of the presence of other substances, such as starch and protein. Raw fibrous material which has not been broken up by chemical treatment, for example, wood pulp, peat, grass and straw, is readily floated by the method according to this invention. -In almost all cases, especially when using an excess of component I, the flotation process does not last longer than sixty seconds and this is an advantage which is the more convincing when it is remembered that for example flotation according to German printed application No. 1,094,570 requires at least half as long again.

Examples In the examples which follow and which in part are arranged in tabular fashion, a definite amount of fibers or fiber slurry, unless otherwise stated, is suspended in 1 liter of water in a cylinder and flotation effected by adding the given amount of components I and II at atmospheric pressure. Air distribution is produced by whirling. As a rule the sequence of addition proceeds in the tables from left to right. In any case deviating from this general rule, numbers in parentheses indicate the actual sequence.

Spontaneous flotation means 100% flotation in less than 15 seconds.

Rapid flotation means 100% flotation in 15 to seconds, the time being measured from the end of the whirling with air.

The fiber slurry used is obtained by grinding unbleached sulfite cellulose in a Rieth beater. Fiber slurry 16 means that unbleached sulfite cellulose has been ground for 16 hours, and Fiber slurry 32 has been ground for 32 hours.

The abbreviations used in the examples have the following meanings:

a=50% of sodium hydroxyoctadecanesulfonate+50% of sodium octadecenesulfonate,

b=oxyethylated castor oil (mole ratio of' castor oilzethylene oxide=lz40 to 1:42),

c=sodium dibutylnaphthalenesulfonate,

d=condensation product of oleyl chloride and methyltaurine,

A=copolymer derived from parts of acrylamide and 30 parts of diethylmethylmethacrylamidomethyleneammoniummethyl sulfate,

B=copolymer derived from 60 parts of acrylamide and 40 parts of trimethylmethacryamidomethyleneammoniummethyl sulfate,

C=copolymer derived from 25 parts of acryl-amide, 25

parts of methacrylamide and 50 parts of dipropylmethyhnet-hacrylamidomethyleneammoniumrnethyl sulfate,

D=copolymer derived from 60 parts of methacrylamide and 40 parts of diethylmethylmethacrylamidomethyleneammoniummethyl sulfate.

The following remarks should be borne in mind in considering the tables:

In Examples 23 to 26, the concentration of component I is varied and that of component II kept constant. In each case complete flocculation with partial to complete flotation takes place.

In Examples 26 to 28, the concentration of component 11 is varied and that of component I is kept constant. The amount of fibers floated in thirty seconds is weighed.

In Examples 29 to 40, the flotation and clarification effects are studied with fiber slurry l6 and fiber slurry 32. The residual turbidity after flotation is measured (P=transmission in percent, measuring instrumient a Zeiss Electrocolorimeter Elko III, 5 cc. cell, filter $5913). The increased requirement of flocculant for the more intensely ground slurry will be noted. In Examples 29 to 31 and 35 to 37, component II is added in one batch; thereafter whirling up is effected at once. In Examples 32 to 34 and 38 to 40, component II is added in portions of 5 mg. After each addition, whirling up is effected ten times. The repeated whirling up and the stagewise addition improve clarification. From this it may be concluded that the flotation flakes obtained according to the process are stable to mechanical action.

Component II Example Fibrous material Component I 1onlc component) Other additions (acrylamide pH Effect v copolymer) 1 0.18 g. fiber slurry 16- 7. 1 Sedimentation. 9 dn 50 mg. resin soap 6. 8 Spontaneous flotation. 2 dn 50 mg. soap 7. 0 Do. 4 do 35 mg. sodium paraflin sulfonate 6. 5 Do.

u-C18)- do 40 mg. a 6. 5 Do. do 40 mg. b 6. 4 Sedimentation. do 50 mg. resin soap 50 mg. alum--." 4.8 Rapid flotation,

1 g. wood pulp mg. resin soap 6. 9 Do. 1 g. unbleached soda pulp 50 mg. resin p 7.0 Spontaneous flotation. 1 g. unbleached sulfite d0 6.8 Do. 1 g. bleached sulfite. 7. 2 Do. W 0.1 g(i waste paper. go 6. 9 Do.

. 0 0 50m alum 4. 7 R id flo t' 14 1 g. bleached straw cellulose d0 g 7. 2 sgt ltane i ls t l otation. 15 do 35(11g. %od)ium paraffin sulfonate 50 mg. alum.-. 4. 6 Do.

u- 18 16 0.5 g. bleached sulfite do 3 ml. n-HCI 5 mg. A 3. 8 Rapid flotation. i; go 56 do T k d u 3 cc. n-NaOH 5 mg. g. 11. 3 Do. 0 mg. or ey re 0 5 mg. 6. 3 Spontaneous flotatiom 19 50 mg. sulfited sperm 011 5 mg. B 6. 3 Rapid flotation.

g. of 'bleached sulfite cellulose having a fineness of grain of 37 SR (Schopper-Riegler) is suspended in 1000 ml. of water in a measuring cylinder and then 1% of resin (as resin glue) and 0.8% of E are added. Clarification from the bottom proceeds at the following rates:

' Seconds: Ml. of clear water l5 28 200 The floated fibers are poured into 8 liters of water and after five minutes the fibers have completely floated again.

Example 43 A paper is prepared from the following raw materials:

65% of bleached sulfite cellulose 35% of bleached sulfate cellulose.

The cellulose mixture is ground to 40 SR. The following amounts of additive, with reference to fibrous material, are also introduced:

I of kaolin 0.005% of ethyl violet 2.0% of sodium abiet'ate and 4.0% of alum.

in which R represents a radical selected from the class consisting of hydrogen and lower alkyl, and in which R R and R; represent radicals selected from the class con- Component II Example Fibrous material Component I (ionic component) Other additions (acrylamide pH Effectv I p copolymer) 0.2 g. fiberslurry 16- 40 mg. 5 mg. B. 6. 6 Spontaneous flotation.

21 -do 40 mg. 0 50 mg. alum 5 mg. B 4. 8 Do. I

22 -do 1 mg. 0 5 mg. C 6. 7 20%flotation in 60".

23 do 2.5 mg. 0.. 5 mg. C 6. 5 60% flotation in 60".

24 do 5 mg. 0 -5 mg. C 6. 5 100% flotation in 10".

25 do 5 mg. 0 1.2 mg. 6. 6 0.046 g. flotation in 26 do 5 mg. n 1.4 mg. 6. 8 0.087 g. flotation in 30".

27 do 5 mg. 0-- 1.6 mg. 7. 0 0.126 g. flotation D130.

29 do 5 mg. 0.- 10 mg. C 6. 8 P=69.0%.

30 do i 5 mg, 0 15 mg. C 7. 0 P=69.0%.

31 do 5 mg. c 5 mg. C 7. 0 P=63.0%.

32 do 5 m ,-o 10 mg. C 6. 7 P=79.0%.

33.-- do 5 mg. 0 15 mg. C 6. 7 P=88.5%.

34 0.2 g. fiber slurry 32. 5 mg. 0 5 mg. C 6. 5 P=26.2%.

36 do 5 mg. 0 15 mg. C 6. 5 P=43.7%.

37 .do 5 mg. 0.. 5 mg. C 6. 7 P=34.5%.

38 do.-- 5 mg. c 10 mg. C 6. 6 P=56.0%.

39 do 5 mg. c 15 mg. C 6. 8 P=70.5%.

40 do 30 mg. d 5 mg. D 6.9 Spontaneous flotation.

41-.. -.do.(1) 30 mg. d (3) 5 mg. D (2)..- 6.8 D0.

Example 42 slstlng of alkyl, hydroxyalkyl and cycloalkyl and m WhlCh two of the radicals R R and R when connected with each other form with the nitrogen atom a heterocyclic fiveto six-membered non-aromatic ring, and in which Y represents the equivalent of an acid radical and (2) copolymers of said quaternary vinyl monomer with up to 99 mol percent of an additional monomer selected from Q the class consisting of acrylamide and methacrylamide;

and floating the fibers by conventional agitation of the fiber suspension.

2. A process as claimed in claim 1 wherein there is added to said suspension about 0.001 to 50% by weight of the fibers of component (A) and about 0.001 to 5% by weight of the fibers of component (B).

3. A process as claimed in claim 1 wherein component (A) is an anionic surface-active compound selected from the group consisting of fatty soaps, dodecylbenzenesulfohate, castor oil sulfonate, alkylnaphthalenesulfonates, alkylsulfonates, sulfitation products of unsaturated fatty acid esters, fatty alcohol sulfonates, condensation products of fatty acid chlorides and methyltaurine, polyhydroxyethylation products having anionic groups, colophony soaps and colophony soaps modified with unsaturated carboxylic acids.

4. A process as claimed in claim lwherein component (A) is a salt of a reaction product of colophony and maleic acid and wherein component (B) is a copolymer of by weight of acrylamide and 30% by weight of the monomer of the formula:

5. A process as claimed in claim 1 wherein component (A) is a salt of a reaction product of colophony and maleic acid and wherein component (B) is a copolymer of 60% by weight of acrylamide and 40% by weight of the monomer of the formula:

eu o-so.

6. process as claimed in claim 1 wherein component (A) is a salt of a reaction product of colophony and A 7 8 naleic agid and wherein lcomgonen ty (t1?) is ahcopfolymtelr FOREIGN PATENTS 0 25 a wei tof ac ami e, 25 0 Wei to meet acryl mid e 2m 50% h weight of the mon mer of the 821 231 fmmla? 530,556 12/1940 Great Britain. m3 9 5 834,410 5/1960 Great Britain. CHFC 9 887,900 1/1962 Great Bntam.

( JONHOHzN- C H1 CHFOSOQ 7 OTHER REFERENCES \(3113 I Stephenson, Pulp & Paper Manufacture, vol. 3, p. 35,

10 published by McGraw-Hill, New York, NY. (1953). I

UNITED STATES PATENTS DONALL H. SYLVESTER, Primary Examiner.

. 0 E V E 2,883,370 4/1959 Price 26080.3 R B RT W MICHA L 2,980,657 4/1961 Melamed 3 15 R. HALPER, H. CAINE, Assistant Exammers.

References Cited by the Examiner 

1. A PROCESS FOR THE FLOTATION OF PAPER FIBERS SUSPENDED IN AN INDUSTRIAL WASTE WATER WHICH COMPRISES: ADDING TO SAID SUSPENSION OF PAPER FIBER (A) AN IONIC SURFACE ACTIVE COMPOUND AND (B) A WATER-SOLUBLE SALT-LIKE POLYMER SELECTED FROM THE CLASS CONSISTING OF (1) THE HOMOPOLYMER OF THE QUATERNARY VINYL MONOMER OF THE FORMULA 